Gas-filled electric incandescent lamp



April 14, 1959 T. MILLNER ET AL 2,882,435-

GAS-FILLED ELECTRIC INCANDESCENT' LAMP Filed Dec. 12, 1957 Fig. 2

AvroRNEYI GAS-FILLED ELECTRIC INCAYDESCENT LAMP Tivadar Millner and Emil Theisz, Budapest, Hungary, assignors to Egyesiilt lzzlmpa s Villamossagi Rszvnytarsasag, Budapest, Hungary, a Hungarian enterprise Application December 12, 1957, Serial No. 702,467

Claims priority, application Hungary December 26, 1956 6 Claim. (Cl. 313-222) This invention relates to gas-filled electric incandescent lamps provided with a coiled tungsten filament and its main object is to obtain an improvement of the quality and of the commercial value of such lamps by efficiently preventing undue occurrence of gaseous elec-' tric discharges in the lamp.

It is well known to those skilled in the art that in gas-filled electric incandescent lamps having a coiled, especially coiled-coil-shaped, tungsten filament gaseous discharges often occur during the burning of the lamp. This occurrence is usually termed in the art as flash-over and may cause the passing of a strong electric current through the gas, the strength of which current highly exceeds that of the current flowing through the filament of the lamp, especially in the case of an arc discharge. This are discharge may assume destructive character by fusing the lead-in wires of the lamp, by cracking the stem through which these wires are passing, by damaging the socket of the lamp and even by destroying the whole lamp in a manner similar to an explosion. This violent arc discharge which, lacking special measures and/or means to prevent this, has destructive effects on the lamp, is often termed in the art as arc-shorting or arcing but will be termed for the sake of brevity and exactness as arc-flashing in the present specification and claims, the expression arc-flashing thus designating the spontaneous occurrence of a violent arc discharge.

In order to prevent the destructive results of arcflashing it is known to provide fuses in the socket of the lamp by shaping a certain part of one or both lead-in wires of the lamp as a fuse dimensioned sons to let the normal operating current ofthe lamp pass without undue rise of temperature, but being promptly fused by the strong current flowing through it on occasion of arcfiashing and thus preventing far-reaching dam-age of the lamp by interrupting its current before it could cause such damage.

It is further well known that up-to-date gas filled electric incandescent lamps are constructed and manu-. factured so as to delay or prevent arc-flashing as far as possible. For this purpose nitrogen, usually in the amount of about 5 to 20 percent by volume, is added to the rare gas or gases used for filling the lamps, and a getter consisting of red phosphorus, or eventually of Sb O is employed in the lamp, and, in addition to these measures, the coiled filament is shaped so as to ensure that the voltage drop taking place in the coiled filament at the rated voltage of the lamp, but measured in the gas-filled space of the lamp along a generatrix of the external cylindrical enveloping surface of the coil, should if possible, not exceed a certain critical value. It is also known to lessen the danger of arc-flashing by filling the lamps with a gas mixture of a pressure surpassing the atmospheric pressure.

During our experiments we have ascertained that the danger of arc-flashing in gas-filled electric incandescent lamps having a gas-filling consisting of one of the wellknown mixtures of one or more rare gases and nitrogen,

States Patent and having, at ordinary temperature i.e. at about 20 C., a pressure lower than the atmospheric pressure, mainly depends on the voltage drop mentioned above as taking place along the coil. We have ascertained that in the actual technical practice of lamps of high-grade manu facture, this danger exists only if this voltage drop, measured in the gas-filled space along a generatrix of the cylindrical enveloping surface of the coil and expressed in volt/min, exceeds a certain critical value. This voltage drop (termed gradient in German) causes the electrical stress to which the gas-filling is subjected in the burning lamp, and breakdown under this stress may cause flash-over or arc-flashing. This voltage drop will therefore be termed, in the present specification and claims, as stress voltage expressed in volt/mm. This stress voltage is, according to the practice of the art, calculated in the case of simply coiled filaments by means of the formula and in the case of coiled-coil filaments by means of the formula wherein G designates the stress voltage in volt/mm, V the rated voltage of the lamp in volts, L the length of the helical single coil, i.e. the length of a generatrix of its cylindrical external enveloping surface in millimetres, n the number of turns of the coil, and d the diameter of the tungsten-wire forming the coil, in millimetres, L the length of the coiled-coil, i.e. the length of a generatrix of its cylindrical external enveloping surface, in millimetres, n the number of the secondary turns, i.e. the turns consisting of simply coiled wire, of the coiled-coil filament and d the external diameter of the primary coil forming said secondary turns in millimetres.

In case of the lamps manufactured and used in previous times the stress voltage of the filament was small, seldom reaching or surpassing 12 volt/mm. and accordingly arc-flashing was a rare occurrence in the case of such lamps if these lamps had been manufactured with due. care and provided with a gas-filling having a sufficiently high pressure'and containing a fairpercentage of nitrogen. Up-to-date lamps however are provided with filament-s having a stress voltage surpassing 12 volt/mm., usually even 15 or even more volts/mm., and it is well known in the art that the danger of arcfiashing is present in these lamps to a very considerable extent.

This invention therefore relates to lamps having a stress voltage of at least 12 but usually 15 or even more. It is, however, to be noted that from the point of view of the danger of arc-flashing not only the stress voltage existing along the coil or coiled coil, which may be calculated by means of the formula disclosed above, has to be considered, but eventually also another stress voltage, which may surpass the stress voltage mentioned above. This other stress voltage exists between any two such points of the filament, the potential difference, i.e. voltage, between which two points at the rated voltage of the lamp surpasses 11 volts and the distance of which points from each other is of such a small value, that the vvalue of the stress voltage calculated by means of the amounts to at least 12. In this formula V designates the potential difference between these two points when the lamp is burning at its rated voltage and L the mutual distance of these two points from each other, the potential difference being volts and the distance millimetres. It is known that such stress voltages may occur in case of such lamps, for example lamps for projection purposes, the simply coiled filament of which is arranged in the lamp not along a straight or arcuate line, but in a more concentrated shape, for example in a zig-zag line wherein parts of the filament are arranged parallel and very close to each other. In such arrangements points of the filament having a relatively high potential difference may be very close to each other. In consequence of this it often can be ascertained that in such lamps the stress voltage, calculated by means of the formula, amounts to a value substantially higher than the value calculated by means of the previously disclosed corresponding formula, amounting often to a multiple of the stress voltage present along a generatrix of the straight part of the simply coiled filament. The danger of arcflashing may therefore be present in such lamps to a substantial extent and may be increased by the high operating temperature of the filaments of such lamps, as it is to be noted that the danger of arc-flashing depends not only on the stress voltage but also on the operating temperature of the filament, on the pressure of the gas-filling and on its kind and composition, especially the ionisation voltage of that rare gas present in the lamp which gas has the lowest ionisation voltage of the rare gases argon, krypton and xenon and is present in the lamp as constituent of its filling gas mixture, i.e. in a substantial percentage of the same.

Experience has shown that it is possible to avoid the above mentioned damaging of the lamps by arc-flashing by using above-mentioned fuses in the lamp but has also shown that it is impossible to avoid by means of such fuses the untimely burning-out of the lamps due to areflashing. Experience has shown that a very substantial percentage of lamps having a stress voltage above 12 respectively 15 burns but owing to arc-flashing before the average rated time of life of the lamp, often after a relatively short life. Although the average life of the lamps of a group comprising a fairly high number of lamps is, as a role, not shortened substantially by some of the lamps burning out after an unduly short life, other lamps of the same group usually having a life surpassing the average life of the lamps of the same group, the premature burning out of lamps nevertheless means a very heavy drawback from a commercial point of view, having a very detrimental effect on the commercial value of lamps of such a make in which premature burning out of lamps is known to occur frequently.

The main object of the present invention is to lessen the danger of arc-flashing in gas filled electric incandescent lamps having a coiled tungsten filament and stress voltages of at least 12 volt/mm.

The invention is based on the discovery that in case of the presence of nitrogen in the gas-filling of the lamp comprising rare gas a surprisingly small addition of hydrogen, also in case of lamps containing a phosphorus getter, is adapted practically to obviate the danger of arc-flashing. Our invention based on this discovery was made by means of overcoming the justified prejudice prohibiting the use of hydrogen in lamps having a tungsten filament.

Adding hydrogen in small quantities to the gas mixture used for filling the lamp has been proposed already more than three decades ago, for the purpose to lessen respectively to prevent sagging of the filament of the lamp. It is therefore known since more than three decades that hydrogen can be used as an additive to the gas-filling of lamps consisting of a rare gas and containing also nitrogen. In spite of this fact the use of hydrogen has been considered, owing to the reasons stated below, to be discarded and was therefore not used in recent technical practice, especially owing to the fact that the use of upto-date tungsten filaments in the lamps has already obviated the danger of sagging of the filaments. The existence of improved tungsten filaments made it possible to construct coiled filaments having a high stress voltage and an increased operating temperature, but this construction of up-to-date filaments caused the danger of arc-flashing which was not present at all in the lamps known and used thirty years ago.

In spite of the fact that the addition of hydrogen to the gas mixture filling the lamp had been proposed long ago, it was considered strictly to be avoided in actual up-todate manufacturing practice. The reason for this general opinion prevailing in the art was partly the knowledge of the fact that the addition of hydrogen impairs the luminous efiiciency of the lamps owing to its good heat-conductivity leading to increased heat-losses, and mainly the knowledge of the fact that already very small quantities of hydrogen are able to cause and constantly to uphold a very noxious circulation of Water vapour in the lamp leading to rapid destruction of the filament and thereby undue shortening of the life of the lamp.

This circulation of water vapour in the lamp is caused by molecules of hydrogen coming into contact with oxides present on some surfaces of some parts of the lamps and reducing these oxides, at the fairly high operating temperature of the lamp, to H O-molecules, as these oxides are apt to be reduced by hydrogen on these temperatures. Even very small quantities of H 0 present in the lamp have the most detrimental elfect of transforming part of the tungsten of the filament to a product which is much more volatile than metallic tungsten and thus consumes the metal of the filament by volatilizing it in an extent highly surpassing that caused by the normal volatilizing of metallic tungsten at the normal operating temperature of the filament. The most series disadvantage is that this process is self-sustaining in the lamp. The water vapour oxidizing the tungsten produces, as a result of this oxidation, hydrogen becoming partly transformed to atomic hydrogen owing to its contact with the tungsten filament of very high operating temperature. This atomic hydrogen is again able to reduce, at the fairly high operating temperatures of the component parts of the burning lamp, oxides present in the lamp and apt to be reduced. Such oxides may be for example the tungsten oxides previously formed by the said action of H 0, the oxide impurities of the surfaces of the metallic parts of the lamps and especially the lead oxide present in the glass parts, for example the glass rod supported by the glass stem of the lamp, consisting of glass containing lead oxide. This oxidation again produces H O which again oxidizes the filament, and so on. By this cyclical process, already very small quantities of H 0 are able to uphold an intensive circulation of H 0 in the lamp and to destroy very soon the filament of lamps having component parts of glass with a content of lead oxide.

It is known to everybody skilled in the art that a very substantial percentage of the electric incandescent lamps presently produced are produced with some parts, for example the rods mentioned above, the lenses integral with these rods, etc., consisting of glass containing lead oxide. This is done because at the fairly high temperatures, amounting for example to 200250 centigrades, to which these parts of the lamps become heated during the operation of the lamps, the insulating properties of this kind of glass surpass those of other similar glasses having no lead oxide content by 4 to 5 orders of magnitude. Owing to these reasons it is easy to understand that in the art of producing up-to-date electric incandescent lamps nobody has thought of proposing an addition of hydro-gen to the gases filling the lamp in order to lessen the danger of arcflashing.

Overcoming this prejudice, we have made a great number of various experiments in order to ascertain the effects of an addition of hydrogen to the gases used for filling the lamps. As a result of these experiments we have surprisingly found that an addition of hydrogen used in lamps filled with rare gases and containing also nitrogen and having a filament of a stress voltage surpassing 12 is, under certain conditions, able to cause a substantial lessening of the danger of arc-flashing amounting practically to the obviation of this danger, without impairing the quality of the lamp, and is even able to cause, in case of employing special measures, an improvement of the luminous eificiency of the lamp without shortening the useful life of the lamp.

The incandescent electric lamp according to the invention and constructed on the basis of our discovery disclosed above therefore has a vitreous bulb containing at least one rare gas, nitrogen and hydrogen and being provided with a coiled tungsten filament having a stress voltage of at least 12 volt/mm, the amount of the said hydrogen content adapted to lessen the danger of arc-flashing, expressed in percent by volume, being between about 0.1 and 1.5, Whereas the amount of said nitrogen content, also expressed in percent by volume, is between about 0.5. and the number. obtained by dividing with 8 the atomic weight of the rare gas having the smallest ionisation voltage among the rare gases argon, krypton and xenon and being present in the bulb as a filling gas, i.e. in a substantial amount, not only constituting an eventual contamination of any of the gases used for filling the lamp, the vitreous bulb of which preferably contains phosphorus as a getter substance. If therefore, for example, the lamp contains only argon as rare gas, the nitrogen content of the gas mixture filling the lamps may be between about 0.5 and 5 percent by volume. If however, the lamp contains also xenon, the aforesaid nitrogen-content may be between about 0.5 and 16.5 percent by volume, as the atomic weight of xenon is 131.3 and xenon has the lowest ionisation voltage of the rare gases used for filling lamps. It is however, also possible to fill the lamps according to the invention with a mixture of several rare gases and in such cases the amount of nitrogen has always to be chosen in consideration of the atomic weight of that rare gas contained in the lamp which has the lowest ionisation voltage.

It is especially advantageous to construct the lamps according to the invention in such a manner, that the surfaces of the parts of the lamps in contact with the gas mixture contained in the bulb should contain no such oxides which can be reduced by hydrogen at the normal operating temperatures of the surfaces in question, which of course have to be devoid of such oxides only to a practical technical extent.

Some of the experimental investigations which have led to our discovery and invention disclosed above and the results of these investigations, as well as some examples of the lamps according to the invention will be described hereinafter in conjunction with the drawings of this specification in order of more particularly detailing the invention.

On the drawings:

Figures 1, 2 and 3 show diagrams containing some results of our experimental investigations, and

Figure 4 shows a side elevational view of an example of the-lamp according to the invention constructed for general illuminating purposes.

The diagrams of Figures 1, 2 and 3 relate to lamps of conventional types constructed for general illumination purposes. The surfaces of some parts of these lamps contacting with the gas mixture filling the lamps have not been devoid of oxides which are apt to be reduced by hydrogen at the operating temperatures of the surfaces in question, as the stern of the lamps consisted of glass containing lead oxide. The filaments of these lamps had stress voltages above as they were shaped as coiled coil filaments and the leadvin conductors of the filaments were provided with fuses contained in the lead-in wires of the lamp in the conventional manner. On the abscissae of these diagrams there are plotted the hydrogen contents of the gas mixture filling the lamps in percent by volume. On the ordinates of the diagrams there are plotted the percentual quantities of the lamps of the examined group which have ended their life by a fusing of their fuses caused by arc-flashing. These diagrams represent the results of the usual burning tests, on occasion of which tests a certain number of identical lamps are being burned at suitable identical constant, for example their rated, voltages until they burn out. The percentual quantity of lamps ending their life owing to arc-flashing is therefore numerical factor adapted to indicate the extent of the danger of arc-flashing as well as the effect of the measures taken for lessening this danger.

Figure 1 of the drawing relates to lamps constructed for a rated voltage of 110 volts and having a luminous output of 40 dekalumen. The pressure of the gas filling the vitreous bulbs of the lamps amounted to 700 Torr (millimetres of mercury column) and the lamps had been gettered in the conventional manner with red phosphorus. The filaments of conventional design had a stress voltage of about 20. The topmost curve of the diagram relates to lamps having a gas-filling of the following composition: 11% H +3% N +(97-n)% Kr, whereas the other curve of the diagram relates to lamps having a gasfilling of the composition: 11% H +6% N +(94-n)% Kr. These lamps had been tested under the same conditions as another group of lamps comprising lamps containing 10% N and Kr, i.e. no hydrogen. This test showed that 95% of the lamps containing no hydrogen but being in other respects absolutely identical with the lamps containing hydrogen ended their life owing to arc-flashing. Figure 1 showing that only 17% of the lamps containing only 6% N but also 0.5% H ended their life owing to arc-flashing, the addition of this small amount of hydrogen thus produced a truly surprising result. By means of extrapolating the lowermost curve of Figure 1 it can be ascertained that in case of adding about 0.7% H to about 6% of N the danger of arc-flashing can already be practically completely obviated, in spite of the fact that the lamp contains only 6% N Such a far-reaching obviation of the danger of arc-flashing cannot be obtained without the addition of hydrogen even by adding in the conventional manner 10 to 13% of N to the krypton. This is shown by the results of the test stated above during which 95% of the lamps containing 10N ended their life by arc-flashing. The lessening of the nitrogen content from the conventional 10 to 13% to the 6% stated above already causes, as well known to those skilled in the art, a substantial lessening of the heat-losses of the filament and thereby an appreciable improvement of the luminous efficiency of the lamps, whereas the heat-losses caused by the small percentage of hydrogen used are quite negligible.

The diagram of Figure 2 relates to lamps containing argon, also constructed for a rated voltage of volts and a luminous output of 40 dekalumen. The composition of the gas-mixture filling the lamp under a pressure of 700 Torr was the following one: 11% H +2% N +(98n) Ar. The topmost curve relates to lamps without a getter of phosphorus, the other curve to lamps containing the usual amount of the conventional phosphorus getter. This diagram shows that in case of lamps containing the phosphorus getter the percentual amount of the lamps ending their life owing to arc-flashing may be reduced by means of an addition of 0.1% H to about 10% and by means of an addition of 0.5% H practically to nil. The conventional amount of nitrogen added to the argon in lamps of this type amounts to 8 percent and therefore the diagram shows that owing to an addition of 0.5% H the addition of nitrogen can be diminished to 2% and arc-flashing nevertheless can be practically obviated, whereby the luminous efficiency and the commercial value of the lamps are increased accordingly.

Figure 3 relates to lamps of the type described in connection with Figure 1, but without a phosphorus getter and without an addition of nitrogen. The composition of the gas-mixture filling these lamps was therefore: 11% H +(ln)% Kr. The diagram shows that in case of such lamps an addition of H is necessary for obviating arc-flashing and an addition of 1% H scarcely has any appreciable efiect as regards the lessening the danger of arc-flashing.

These experimental results therefore clearly show the favourable effect of an addition of hydrogen in the presence of nitrogen, especially in case of lamps containing a phosphorus getter. In order to ascertain the extent to which an addition of hydrogen lessens the luminous efiiciency of the lamps owing to the high heatconductivity of hydrogen further examinations have been effected.

For this purpose lamps of the type described in connection with Figure l have been tested to their average luminous efiiciency by means of the conventional burning test, the examined lamps containing hydrogen in amounts ranging from 0.1% to 5%. The luminous efliciency was calculated from the test results of the individual lamps for an average life-time of 1000 hours and expressed in lm./watt. These experiments have shown that the luminous efficiency thus ascertained begins to decrease, in an extent apt to be measured by means of conventional methods, in case of additions of hydrogen amounting to about 1.5% and further decreases with the increase of the amount of hydrogen added. A decrease apt to be measured by means of conventional methods designates a decrease of at least 0.5 of the luminous efficiency expressed in lm./watt and calculated to the average life time of 1000 hours.

These experiments have also shown that in case of lamps provided with an addition of hydrogen less than about 0.5% the luminous eificiency began to decrease again with further decreasing of the amount of the added hydrogen. This phenomenon appears to be bafiling at first sight, but we have ascertained that it can be explained on the basis of the results of our experiments previously disclosed by taking into consideration the fact that an addition of hydrogen in an amount less than 0.5% is not sufficient any more in case of these lamps containing only 6% N for a satisfactory lessening of the danger of arc-flashing. Therefore a not negligible number of the examined lamps, the percentage of which may be ascertained from the diagram, ends its life prematurely owing to arc-flashing. If these lamps would have had their rated length of life, for example 1000 hours, they would have increased the average luminous efficiency of the lamps of the examined group, as this luminous efliciency was calculated as an average for the average rated life of 1000 hours of the lamps of the examined groups. These examinations therefore show that by means of a suitable addition of hydrogen even the luminous efficiency of the lamps can be improved owing to the lessening of the danger of arc-flashing obtained by means of this addition of hydrogen. This improvement, however, is only possible if the quantity of the hydrogen addition is chosen in such a manner that the increasing of the average elfective life time of the lamps obtained by the lessening of the danger of arc-flashing, i.e. the improvement of the average luminous efficiency obtained thereby, together with the lessening of the heat losses obtained by the lessening of the nitrogen content of the gas mixture filling the lamp, surpasses the decreasing of the luminous efficiency caused by the high heat-conductivity of hydrogen. Our experiments have shown that on the basis of some preliminary experiments the ascertaining of such an optimum amount of the addition of hydrogen is possible in the case of the overwhelming majority of types of lamps, especially if the lamps in question are devoid 8 of the oxides mentioned above apt to be reduced by hydrogen.

We have ascertained and it may be seen already from the diagrams of the drawing, that this favourable range of the quantity of the hydrogen addition depends also on the quantity and quality of the rare gas contained in the lamp as well as on the quantity of nitrogen present in the lamp. Figure 3 shows that in the absence of nitrogen about 5% of H have to be added in order to obviate the danger of arc-flashing and this quantity of hyrogen already causes a decrease of the luminous efliciency exceeding that caused by the conventional addition of 13% of nitrogen. If however, according to the invention, a suitable part, for example one-half, of the conventional percentage of nitrogen is substitued by krypton and the increased danger of arc-flashing thereby caused is obviated by means of adding a small quantity, for example 0.5 of hydrogen, an improvement of the luminous efficiency is obtained as a final result, as already mentioned above. The same favourable result can be obtained also in case of lamps filled with argon by means of adding, instead of the conventional amount of about 8% used for these lamps containing coiled-coil filaments, only about 1 to 3% of nitrogen together with an addition of hydrogen amounting for example to 0.5

If however the percentage of hydrogen exceeds a certain small value depending on the type of the lamp in question, the favourable effects of this addition of hydrogen appear as a final result only if the surfaces of the parts of the lamp in contact with the gas-mixture filling the lamp are devoid of the oxides mentioned above as apt to be reduced by hydrogen at the operating temperature of said surfaces. In order to construct such lamps the simplest expedient is to make the glass parts in question from a kind of glass which contains no lead oxide, and to clean the metallic parts contacting with the gas-mixture carefully, for example by means of electrolytic processes well known in the art. It is however also possible to coat the surfaces in question with protective coatings devoid of oxides apt to be reduced by hydrogen at the operating temperatures of the surfaces in question. For this purpose it is for example possible to coat the rod and the lens integral therewith, both consisting of glass containing lead-oxide, with a coating of silicon dioxide.

As a result of what has been said above, the invention provides the new teaching that on occasion of manufacturing gas-filled electric incandescent lamps having such a construction that the stress voltage existing in the lamps surpasses 12 volt/mm, such a quantity of hydrogen has to be added to the gas-mixture present in the lamp which is sufficient practically to obviate the danger of arc-flashing in presence of a relatively small percentage of nitrogen, whereby the nitrogen content may be lessened substantially below the amount necessary in case of the absence of hydrogen and in consequence may partly be substituted by rare gas, the percentual amount of rare gas thus being increased as regards to the quantity conventionally used up to now. If the amount of hydrogen which has to be used according to this teaching would already cause the above mentioned objectionable results of the formation of H 0 in the lamp, the

lamp has to be constructed in a manner to have the surfaces of its parts contacting with the filling gas mixture devoid of oxides apt to be reduced by hydrogen at the operating temperature of the lamp.

The following Examples 1 and 2 show the manner of ascertaining the most favourable percentage of hydrogen, which can always be ascertained by means of some preliminary experiments and depends mainly on the type of the lamp in question. These examples, as Well as the following ones, relate to lamps of conventional types, it being however understood that the invention is not limited anyways by any of these examples.

9 Example 1' Gas-filled electric incandescent lamps constructed for general illumination purposes and rated voltages of 110 volts, having an energy consumption of 40 watts, a coiled-coil tungsten filament of the kind conventionally used in lamps containing krypton and having therefore a stress voltage of about 20, have been filled with gas at a pressure between 650 and 700 Torr, gettered with the conventional phosphorus getter and provided with glass rods and lenses containing no lead oxide. Fifteen such lamps have been filled with the conventional gas mixture consisting of 87% Kr and 13% N and fifteen other such lamps with a gas mixture consisting of 93.5% Kr, 6% N and 0.5% H The conventional burning test of these lamps, all of which were provided with the conventional fuses, showed the following results:

Lamps of the type according to Example 1 but provided with a conventional coiled-coil filament constructed for lamps filled with xenon and having a stress voltage of about 18, had been gettered with phosphorus in the conventional manner and provided with glass rods and lenses containing no lead oxide. These lamps constructed also for a rated voltage of 110 volts and an energy consumption of 40 watts, were tested by filling fifteen lamps with the conventional gas mixture consisting of 87% Xe and 13% N and fifteen identical lamps with a gas mixture consisting of 86.2% Xe, 13% N and 0.8% H and subjecting them to the conventional burning test, the results of which have been the following ones:

Luminous Average Arcefficiency life time Lamp flashing, for 1,000 at rated percent hours, voltage,

lrn/w. hours Known 100 14. 7 960 New 10 14. 8 1, 030

Example 3 We have found that in krypton lamps of conventional design constructed for general illuminating purposes and rated voltages not surpassing about 170 volts, and being generally between 110 and 130 volts, it is possible, when using the conventional construction of the coiled-coil filament resulting in stress voltages between about 13 and 15, the conventional gas pressure ranging between about 600-700 Torr and the conventional gettering by means of a phosphorus getter, but using glass parts containing no lead oxide, it is possible to reduce the conventional amount of 13% of nitrogen to amounts ranging between 8 and 3%. Lamps according to the invention thus constructed have been found to be practically free from the danger of arc-flashing and to have a luminous efliciency surpassing that of identical lamps of the conventional type, i.e. containing about 13% N but no hydrogen, by

at-least 0;5% oftheluminous etficiency of theseknown lamps.

Example 4 In case of the lamps of the type described in Example 3, but constructed for rated voltages above 170 volts, for example 220-240 volts, and accordingly provided with filaments having stress voltages ranging between about 16.5 and 18, an addition of hydrogen ranging between 0.2 and 7% made it possible to diminish the conventional amount of 13% N to amounts ranging between 9 and 4% with the results stated in Example 3;

Example 5 In case of the lamps of the type described in Example 3, but constructed for being filled with argon and accordingly provided with coiled coil filaments having stress voltages ranging between about 19.5 and 21, an addition of hydrogen ranging between 0.1 and 0.5 made it possible to diminish the conventional amount of 8% N of the gas mixture of these lamps, constructed for rated voltages below 170 volts, to amounts ranging between 3 and 1% with the results stated in Example 3.

Example 6 The lamp shown by Figure 4 of the drawing is a lamp of conventional design, constructed for general illuminating purposes and a rated voltage of 220 volts. The glass bulb 1 of the lamp, consisting of the usual kind of glass, has the conventional shape but contains, under a pressure of 660 Torr, a gas mixture consisting of 97.5% argon, 2% nitrogen and 0.5% hydrogen. The coiled-coil shaped filament 2 of tungsten wire is of conventional construction and accordingly has a stress voltage of 22.5, itsenergy consumption being 40 Watts at the rated voltage. The glass rod 3 and the lens 4 integral therewith consist of glass containing no lead oxide, whereas the glass of the stem 5 and the exhaust tube 6 may contain lead oxide. The conventional socket 7 of the lamp has its base contact 8 connected to the lead-in wire 9 connected to the filament lead-in wire 10, and the lead-in wire 11 is connected to the filament lead-in wire 12. Both of the lead-in wires 9 and 11 are constructed in the conventional manner, so as to contain parts adapted to act as fuses. The filament support wires 13 and 14 are of conventional design. In spite of its nitrogen content of only 2% instead of the conventional 8% this lamp is, owing to its content of 0.5% hydrogen, practically free from the danger of arc-flashing and has a luminous efiiciency of 11.4 lumen/watt, whereas the luminous efiiciency of the conventional lamps of this type is only about 10.9 lumen/ watt.

Lamps of the same type, but constructed for other rated voltages also surpassing 170 volts and for other energy consumptions and accordingly having filaments with stress voltages ranging between about 22.5 to 28 may have a content of hydrogen ranging between 0.1 and 0.5% and nitrogen contents ranging between 5 and 2%, and also show improvements similar to those stated in Example 3.

Example 7 In case of lamps of the type described in Examples 3 and 4, but constructed for being filled with xenon and having rated voltages ranging between about and 250 volts and accordingly stress voltages ranging between about 18 and 22, an addition of hydrogen ranging between 0.4 to 0.9% enables the lessening of the conventional percentage of 25 to 30% of the nitrogen content to Values ranging between about 16 and 8% with the results stated in Example 3.

In connection herewith it is to be remarked that the expression practically free from the danger of arc-flashing contained in Examples 3 and 6 and in other parts of this specification means that the percentage of the lamps ending their lifte in consequence of arc-flashing lies below to percent of the number of the examined lamps.

It is further to be remarked that the lessening of the danger of arc-flashing obtained according to the invention results also in a considerable lessenting of the dif-' ferences between the lifetimes of the individual lamps and thereby in an increasing of the commercial value of the lamps owing to the reasons already stated above. It is well known that the average of lifetime of say 1000 hours is the average value of the lifetimes of the individual lamps of a group of lamps comprising a substantial number, for example 1000, lamps, the individual lifetime of these lamps ranging between rather wide limits of for example 500 to 1500 hours owing to the scattering, unavoidable in actual manufacturing practice, the lifetimes of the individual lamps. One of the reasons of this irregularity is, besides the unavoidable tolerances of manufacture, the arc-flashing occurring after very difierent periods of time during the lifetimes, of the individual lamps. If now it is assumed, for the sake of an illustrative example, that in case of an average lifetime amounting to 1000 hours 60% of the individual lifetimes are be tween 900 and 1100 hours, it is obvious that this Very important percentage of 60% of the same group of lamps may be substantially increased, even to about 90%, by obviating one of the important reasons of the aforesaid dilferences between the individual lifetimes, i.e. arc-flashing. In this case the probability that the average life time of the lamps of a small group comprising for example only ten lamps indeed amounts to 1000 hours is substantially increased, whereby the commercial value of the lamps is also increased.

In connection with the examples it has to be stated that the invention is not limited to lamps described in these examples as its teachings can be applied to a great variety of gas-filled electric incandescent lamps having coiled tungsten filaments with stress voltages above 12 and containing a rare gas and nitrogen. It is for example possible to use in the lamps according to the invention, especially in lamps constructed for special purposes, filaments constructed and/ or arranged so as to have stress voltages exceeding the conventional ones, for example in order to produce filaments of smaller bulk and therefore lessened heat losses and/ or filaments for emitting concentrated light from a very small surface, and it is also possible in some cases of special lamps to omit the fuses conventionally used in lamps having high stress voltages. The gas mixture may contain a plurality of rare gases, for ex ample if the lamps are filled with the mixture of krypton and xenon obtained on producing these rare gases from atmospheric air. The nitrogen as well as the hydrogen may be added to the rare gases used for filling the lamps also in the shape of suitable compounds, such as for example NH or HN as the desired relation between the amounts of nitrogen and hydrogen present in the lamps may easily be adjusted by adding also pure H and/ or N to the gas mixture. In the lamps according to the invention it is also possible to use other getter substances besides or instead of the phosphorus mentioned above. In consequence of what has been said above, the teachings of this invention may be applied to a very great variety 12 of lamps and thus lamps of almost any desired type may be produced according to this invention and without the loss of its benefits.

Having now particularly described and ascertained the,

nature of our invention and in what manner the same is to be performed, we declare that what we claim is:

1. An electric incandescent lamp comprising, in combination, a vitreous bulb filled with a gas mixture containing a rare gas and nitrogen, and a coiled tungsten filament of a stress voltage surpassing 12 volts/mm. inside said bulb, the percentage by volume of the ultra gen content of said gas mixture ranging numerically between about 0.5 and the number obtained by dividing with 8 the number indicating the atomic weight of the rare gas having the lowest ionisation voltage amongst the rare gases argon, krypton and xenon and being present in said bulb as a filling gas, said gas mixture also containing hydrogen in an amount adapted to lessen the danger of arc-flashing and ranging between about 0.1 and 1.5 percent by volume.

2. An electric incandescent lamp comprising, in combination, a vitreous bulb filled with a gas mixture containing a rare gas and nitrogen, and a coiled tungsten filament of a stress voltage surpassing 12 volts/mm. inside said bulb, the percentage by volume of the nitrogen content of said gas mixture ranging numerically between about 0.5 and the number obtained by dividing with 8 the number indicating the atomic weight of the rare gas having the lowest ionisation voltage amongst the rare gases argon, krypton and xenon and being present in said bulb as a filling gas, said gas mixture also containing hydrogen in an amount adapted to lessen the danger of arcfiashing and ranging between about 0.1 and 1.5 percent by volume, said lamp comprising parts having surfaces contacting with said gas mixture and said contacting surfaces being practically devoid of oxides apt to be reduced by said hydrogen content at their operating temperatures prevailing during operation at said rated voltage of said lamp.

3. An electric incandescent lamp as claimed in claim 2, comprising vitreous parts contacting with the gas mixture filling said lamp and containing no lead oxide.

4. An electric incandescent lamp as claimed in claim 2 comprising a glass rod and lens for supporting the filament of said lamp, said rod and lens containing no lead oxide.

5. An electric incandescent lamp as claimed in claim 2, comprising a glass stem bearing a glass rod and a glass lens for supporting the filament of said lamp, said stern,

. rod and lens containing no lead oxide.

6. An electric incandescent lamp as claimed in claim 1,154,514 1,572,670 Myers Feb. 9, 1926 1,656,957 Schroter Jan. 24, 1928 Jacoby Sept. 21, 1915 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,882,435 April 14, 1959 Tivadar' Niillner at al,

is hareby certified that errcr appears in the above numbered patent requirimg corraction and that the said'Letters Patentshould read as cor recued below.

llazaafiing "so the" printed. specification, line 8, for the priority date "fiacember 2'6, 1956" read; December 22'; 1956-,

,sealfi this 1303 day of Octbber 1959,

(SEAL) Atfiest;

N, L Ll I MR m ROBERT c. WATSON Attesting .offic er Conmissioner of Patents 

